Autorotator kite



Se t. 1, 1970 A. FLATAU AUTOROTATOR KITE Filed May 22, 1967 United States Patent 3,526,377 AUTOROTATOR KITE Abraham Flatau, Joppa, Md. (P.O. Box 657, Edgewood, Md. 21040) Filed May 22, 1967, Ser. No. 640,243 Int. Cl. 1364c 31/06; A63h 27/08 US. Cl. 244-153 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an improved autorotator which comprises in cross section a high efficiency lift airfoil rotationally transformed. A pair of airfoil members 'based on the rotationally transformed airfoil are positioned with their undersides generally face to face with the trailing edge of each airfoil member positioned at about the center line of the undersurface of the other airfoil member An improved kite is formed with these airfoil members and oversized end plates having central bearing members for attachment of stationary tethering members.

The present invention relates to an autorotator or autorotor. More particularly the present invention relates to a structure mounted for rotation about a longitudinal axis particularly adapted to employment as part of a rotating wing kite and in other devices involving autorotation or fluid flow.

Numerous rotatable airfoil kites of various specific airfoil shapes have been suggested to the art. Such structures usually comprise an axially elongated airfoil structure with end plates or a center plate fixed thereto. Suitable bearing structure is provided at the longitudinal or span ends, e.g., in the end plates, through which stationary tethering means are attached. Characteristically, the airfoil itself and the assembly as a whole, constitute a relatively inefiieient aerodynamic lift device. In consequence, prior art autorotatable kites have required strong winds for lifting the kite and have exhibited some dimensional and aerodynamic instability.

The object of the present invention is to provide an improved autorotator or autorotor.

A further object of the present invention is to provide an improved kite which exhibits high aerodynamic efii cieney.

Still another object of this invention is to provide an autorotatable kite of high lift ability and good flight stability.

Other objects and advantages of the present invention will become more apparent from the description thereof which follows.

Referring now to the drawing wherein:

FIG. 1. is a perspective view of the present autorotator with one end broken off;

FIG. 2 is a front view of a autorotatable kite constructed according to the practices of the present invention;

FIG. 3 is a plan view of an end plate, and is taken along lines 33 in FIG. 2; and

FIG. 4 shows a typical high lift efficiency airfoil and its rotational transformation.

The basic autorotator is formed by a pair of properly curved airfoil members 12 and 14 fixedly mounted at their span ends in end plates 16 and 18.

The kite structure v11, as shown in FIG. 2, further includes bearing members 20 and 22 disposed respectively at the center of end plates 16 and -18 and stationary arms 24, '26 mounted in the bearings 20, 22 so that the auto rotator may freely rotate around the stationary arms (e.g., of wire) 24 and 26. Arms 24 and 26 may terminate at a yoke member 28 to which is connected the tethering string 30.

3,526,377 Patented Sept. 1, 1970 Curved airfoil members 12 and 14 are of a special shape and must be associated together properly. They form the heart of autorotator 10 and of kite 11.

The term airfoil as employed herein is used in a strict sense to indicate the cross section of a wing, but since members 12, 14 are not wings (as in a glider or airplane) they are referred to herein as airfoil members. However, the detailed form of airfoil members 12, 14 are derived from wing counterparts, as hereinafter explained.

The actual shape of airfoil members 12, 14 may be best understood from consideration of FIG. 4, which shows a typical high lift efficiency airfoil (Clark Y airfoil). Airfoils, as such, have been investigated and reinvestigated by the art. Whole families of airfoil curves have been 5 suggested (e.g., N.A.C.A. 22-, 44-, 230-serie's, the Munk series) with some individual airfoils of note being N.A.C.A. 23102, the Clark Y, and the Davis airfoil. As a starting point for the present autorotator, then, any high lift efficiency airfoil may be employed, and one such typical airfoil has been illustrated in FIG. 4. The basic airfoil once selected is then converted from orthogonal (x, y) coordinates to polar coordinates, and then transformed by several ways, e.g., by the classical method known as conformal mapping. Actually, a man skilled in the art can approximate the transformed airfoil without resorting to the theoretical equations, through the use of a cosine function multiplication of the polar coordinates. During this single valued transformation every point on the original airfoil is transformed to a corresponding point 0 of a newly formed (more highly curved) airfoil. However, in making the transformation (or afterward), the sharp trailing edge characteristic of high efficiency airfoils is rounded off to provide a curved or rounded edge (whose original orthogonal counterpart 36') is shown in shadow form in FIG. 4. If too angular, the leading edge may also be made more rounded. The airfoil members 12, 14 shown in the drawing correspond then to a single valued transformation of the wing based upon the airfoil of FIG. 4. Top surface 34, bottom surface 32, leading edge 37 and trailing edge 36 are then the airfoil curves 32', 34', the leading edge 37, and the trailing rounded off edge 36', transformed. The transformation placed trailing edge 36 about from leading edge 37.

In effect, what is done is to rotationally transform any high lift eificiency airfoil from an airfoil designed for linear movement to a corresponding shape intended for rotational movement by maintaining a point to point re lationship through single-valued transformation. This conversion is herein referred to as a rotational transformation. Essentially, the rotationally transformed new airfoil is as suitable for rotational movement as the original was for linear movement. Correspondingly, airfoil members 12 and 14 are as suitable for rotation as the corresponding wing is for linear movement.

As shown in FIG. 1, the two airfoil members 12 and 14 are positioned in spaced apart relationship with trailing edge 36 of airfoil 14 disposed at about (i.e., within 10%) the center line to lower surface 32 of airfoil 12. Trailing edge 36 of airfoil 12 is similarly positioned centrally of airfoil 14. The rotational axis 38 of autorotator 10 then passes essentially midway between the two trailing edges 36. The chordal diameter 39 of the autorotator 10 (FIG. 3) is greater (by about 50%) than the distance from leading edge 37 to trailing edge 36 of either airfoil member.

The above described interpositioning of airfoil members 12, 14 is important to proper operation of autorotator 10. The channel for air flow between members 12, 14 approximates a constant cross-sectional channel which causes the inner air flow to undergo a minimum of acceleration and a minimum of pressure changes and disturbances inside this channel. Therefore, as a point of preference, high lift efiiciency airfoils which do not deviate excessively from the single-camber type become preferred as basis for transformation into airfoil members 12, 14. Transformation of a highly curved double camber type of airfoil causes the central channel (between members 12, 14) to deviate appreciably from the desired constant cross-sectional area.

The above described interposition of airfoil members 12 and 14 underlies the importance of avoiding a sharp trailing edge on these members. Presence of a sharp trailing edge is accepted in airfoils and wing construction, virtually as mandatory for obtaining a well defined lift (on the basis of the circulation theory). However, the rationale of fixed attitudes or angles of attack which exist for wings, is not present in a structure producing continuous autorotation when subjected to an air stream. At fixed attitudes or angles of attack, the sharp trailing edge of a typical high lift efliciency airfoil produces a bound vortex. However, under rotation, i.e., autorotation, the same sharp trailing edge produces separated flow which then results in added drag. Hence, the rounded off trailing edge 36 of the rotationally transformed airfoil is important to the present structure, providing several advantages, i.e., reduced drag and a smoother inlet and outlet for the flow channel between airfoil members 12, 14.

The curved leading edge 37 and the airfoil shape as a whole of members 12, 14 contribute most importantly to autorotation by providing a high pitching moment and static torque as well as the high lift (during rotation) efficiency characteristic for which the airfoil was selected originally. The upper surface curvature 34 which induces high suction pressures on these outer surfaces is significant toward obtaining a high peripheral to free stream velocity ratio (otherwise known as u to V ratio). Furthermore, the high 11/ V ratio is directly related to the magnitude of magnus lift. (This is the lift force resulting from autorotation.) In short, the airfoil genesis of outer surface 34 facilitates production of very high lift forces (compared to the results attained with prior art shapes). In addition, the channel between the two airfoil sections 12 and 14 with its approximately constant crosssection acts to reduce the overall drag of autorotator as does presence of a rounded trailing edge 36. In consequence the detailed structure of autorotator 10 offers the highly desirable combination of high magnus lift and minimized drag, i.e., a high lift to drag ratio, and the autorotator consequently exhibits an excellent angle of flight. As a practical matter, the kite will fly much closer to the vertical than less eflicient structures, and will initiate lift at lower wind velocities.

Still another facet of the above described structure, one which adds significantly to a high lift to drag ratio, is presence of circular end plates 16, 18. The improvement added by their presence more than makes up (in a kite) for the drag added by the weight and the form drag of the end plates 16 and 18. The plates themselves should, of course, be associated with airfoil members 12, 14 normal to axis 38 and symmetrical therewith as is shown in the drawing. In addition, end plates 16, 18 should have a substantial diameter, i.e., a diameter at least 50% greater than the length of chordal line 39.

End plates 16 and 18 may be formed with a recess or an overlapping segment matching the curved airfoil contour to allow insertion of airfoils 12 and 14 therein and locking (e.g., glued) of the total into a rigid structure. FIG. 3 shows recesses 40 and 42 which match the size and shape of airfoil members 12, 14 to receive and lock them to the end plate 16. Similar recesses (not shown) are present on end plate 18. The substantial area of contact between the airfoil members 12, 14 and recesses 40, 42 on end plates 16, 18, together with the enclosed character of airfoil members 12 and 14, make the four member structure (of 12, 14, 16, 18) a rigid unitary structure of substantial flexural and torsional strength.

Airfoil members 12 and 14 may be fabricated by extruding a light weight thermoplastic resin (e.g., polyethylene) as a hollow thin walled section into appropriate lengths. In order to maintain overall rigidity the extrusion section may include internal ribs (not shown) extending from surface 34 to surface 32. Similarly, end plates 16 and 18 may be stamped or blow molded using the same light Weight thermoplastic resin. Fabrication of the various component members of autorotator 10 out of plastic permits a simple assembly through a press fit (and glue) of foil sections 12 and 14 into recesses 40 and 42 on end plates 16 and 18.

Free flight and wind tunnel experiments have shown that certain parameters within the purview of the above described construction are important to the performance of the autorotator. One such parameter is the aspect ratio, i.e., the ratio of the span (based on rotational axis line 38) to the length of chordal diameter line 39 (chord). Increasing the aspect ratio serves to increase the glide angle or, expressed otherwise, the lift to drag ratio (principally through reduction of drag per unit span). Still another parameter contributing to improvement (of the glide angle and stability) of the autorotator is the size of end plates 16, 18. Mention has already been made that providing end plates of a diameter at least 1.5 times the basic chord length 39 serves to improve the lift to drag ratio (as compared to smaller end plate); the end plates also improve the dynamic stability of the autorotator.

Ornamentation of kite 11 is contemplated. Thus airfoil members 12 and 14 may be made striped or varicolored to achieve a flying barber pole effect visible at great distances. Also contemplated is provision of a cluster of kites for which instance wires 24, 26 from several kites may be attached to the same yoke 28 or tied at spaced apart locations on the same tethering cord 30.

The foregoing description of the autorotator structure has been posed almost entirely in terms of a kite, a plaything. However, the detailed structure described above, i.e., airfoil members 12, 14 with or without end plates 16, 18 are capable of practical utility. For example, mounting an electric motor to drive airfoil members 12, 14, may convert the unit into a pump. Still another use contemplated with autorotation or with motor impelled rotation, employs the otherwise empty space inside airfoil members 12 and 14 (through suitable fluid flow connection at end plate 16 or 18) and apertures in surfaces 32, 34 to feed fluid into the stream (of air) in which the autorotator revolves. The high degree of vorticity and turbulence downstream of airfoil sections 12, 14 makes for excellent admixture between the flowing stream and whatever fluid enters by Way of the apertures in surfaces 32, 34 of airfoil members 12, 14. In this or related fashion, autorotator 10 may feed water into an air stream for humidification purposes.

Still further practical uses for the present autorotator as may suggest themselves to skilled workers in the art are contemplated within the scope of the appended claims, as are routine modifications in the kite embodiment herein shown and disclosed.

What is claimed is:

1. An autorotator comprising a pair of elongated hollow airfoil members disposed in spaced apart relation and a circular end plate at each axial terminus thereof, each airfoil member comprising in cross-section a high lift efficiency airfoil upper surface having a high lift to drag ratio and an essentially semicircular lower surface, said airfoil members being disposed with the trailing edge of each airfoil member positioned at about the center line of the under surface of the other airfoil member, said under surfaces thereby being in a generally face to face relation.

2. The autorotator of claim 1 wherein the end plate diameter is at least 1.5 times the chordal line extending from the leading edge of one airfoil member to the leading edge of the other airfoil member.

3. A kite constructed with the autorotator of claim 2 wherein bearing members are provided centrally of each end plate and stationary tethering means are secured in said bearing members, said tethering means being adapted for attachment to an extended string.

4. An autorotatable structure comprising a pair of hollow airfoil members, each said member being in cross section a high lift efliciency airfoil having a high lift to drag ratio rotationally transformed the leading edge of the transformed airfoil being about 180 from the trailing edge of the transformed airfoil, and the trailing edge being rounded 01f, the underside of the transformed airfoil being essentially a semicircle, said airfoil members being disposed with the trailing edge of each airfoil member being positioned at about the center line of the under surface of the other airfoil member, said under surfaces thereby being in a generally face to face relationship.

5. An autorotatable structure as in claim 4 wherein circular end plates are positioned at the axial terminals of said airfoil members, the diameter of each end plate being at least 1.5 times the chordal line extending from the leading edge of one airfoil member to the leading edge of the other airfoil member.

References Cited UNITED STATES PATENTS MILTON BUCHLER, Primary Examiner P. E. SAUBERER, Assistant Examiner U.S. Cl. X.R. 

